Ultra-thin gate dielectrics

ABSTRACT

An in-situ ultra dilute ammonia nitridation process and apparatus of the following ultra-thin chemically tailored gate dielectrics: DCE/O 2  (Trans 1,2-Dichloroethylene) based ultra-thin gate dielectric; Nitric Oxide (NO) based ultra-thin gate dielectric that has been re-oxidized via a DCE/O 2  (Trans 1,2-Dichloroethylene) process; “dry-wet” DCE (Trans 1,2-Dichloroethylene)/O2-H2O/O2) based ultra-thin gate dielectric; and ultra dilute, less than 1E-7 moles NH 3 /mm 2 , nitridation of an ultra-thin gate dielectric. A vertical diffusion furnace (VDF) is provided to process the same. The ultra-thin chemically tailored gate dielectrics generated in a VDF with ultra-dilute NH 3 , below 1E-7 moles NH 3 /mm 2 , in-situ nitridation show a performance comparable or better to traditional ex-situ rapid thermal anneal (RTA) processing techniques for 90 nm CMOS technology. These methods replace and remove at least one process layer in the fabrication of CMOS devices using traditional ex-situ RTA processing, decreasing production costs, and improving fabrication cycle time, with equivalent or improved transistor performance.

FIELD OF THE INVENTION

[0001] The present invention relates to microelectronic device fabrication and, more particularly, to gate dielectrics for semiconductor devices.

BACKGROUND OF INVENTION

[0002] In the fabrication of semiconductor devices, the semiconductor substrate undergoes a number of thermal processes some of which are performed in two separate apparatus. Batch furnaces, such as vertical diffusion furnaces (VDF), are capable of processing 100-200 substrate simultaneously and are used predominantly for well drive-ins, field oxidation, and gate oxidation of films thicker than about 100 nm. Rapid thermal processors (RTPs) process one wafer at a time and are used predominantly for silicidation, nitridation, SiO₂ anneals, and gate oxidation for films under 100 nm.

[0003] In front-end processing, gate oxidation is usually considered the most critical oxidation application, as required gate oxide thickness' shrink from 40-50 nm for the 0.25 μm devices to 30-40 nm for 0.18 μm devices and 20-30 nm for 0.15 μm devices. Due to currently available batch furnace limitations, RTPs are used for the ultra-thin, below 100 nm, dielectric gate oxidation and nitridation.

[0004] Incorporating nitrogen into the gate oxide, known as nitridation, is an important step in fabrication of an ultra-thin gate dielectric. The incorporation of nitrogen degrades low-field electron mobility, increases high-field electron mobility, improves charge to breakdown, and increases fixed positive charge, among others.

[0005] Rapid thermal processors provide dedicated equipment that can provide the precise level of process control required for ultra-thin gate oxidation layers, and in particular, nitridation of the gate oxide. Rapid thermal processors provide faster temperature rise times and more precise temperature uniformity than batch furnaces, which provides the necessary control.

[0006] In order to increase through-put and reduce operating times and costs, it is desired to provide gate oxidation and nitridation in-situ and in sequence with other processes using the batch furnace. There is potential to reduce the number of thermal cycles, processing steps, and the cost of equipment if gate oxidation and nitridation can be performed in the batch furnace.

[0007] New apparatus and methods are needed for providing an ultra-thin nitrided gate dielectric in an in-situ process using a batch process.

BRIEF DESCRIPTION OF DRAWINGS

[0008] FIGS. 1A-C are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin DCE/O₂ (Trans 1,2-Dichloroethylene) based gate dielectric, in an embodiment in accordance with the invention;

[0009] FIGS. 2A-D are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin nitric oxide (NO) based gate dielectric, in an embodiment in accordance with the invention;

[0010] FIGS. 3A-D are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin “dry-wet” DCE/O₂—H₂O/O₂ based ultra-thin gate dielectric, in an embodiment in accordance with the invention;

[0011] FIGS. 4A-D are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin “dry-wet” DCE/O₂—H₂O/O₂ based ultra-thin gate dielectric, in another embodiment in accordance with the invention;

[0012]FIGS. 5A and 5B presents graphs of data comparing the performance of DCE-based gate oxide in-situ nitridation and chemically tailored “dry-wet”-based gate oxide with in-situ nitridation, respectively, with the performance of traditional ex-situ rapid thermal anneal (RTA) processing; and

[0013]FIG. 6 is a cut-away view of an embodiment of a vertical diffusion furnace in accordance with the present invention.

DESCRIPTION

[0014] In the following detailed description, reference is made to the accompanying drawings which form a part hereof wherein like numerals designate like parts throughout, and in which is shown by way of illustration specific embodiments in which the invention may be practiced. It is to be understood that other embodiments may be utilized and structural or logical changes may be made without departing from the scope of the present invention. Therefore, the following detailed description is not to be taken in a limiting sense, and the scope of the present invention is defined by the appended claims and their equivalents.

[0015] In the following methods, in accordance with embodiments of the present invention, ammonia (NH₃) is used as the nitrogen (N) source in in-situ processes for the nitridation of ultra-thin chemically tailored gate dielectrics.

[0016] FIGS. 1A-C are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin DCE/O₂ (Trans 1,2-Dichloroethylene) based gate dielectric, in an embodiment in accordance with the invention.

[0017]FIG. 1A is a side view of a Si semiconductor substrate 10. The substrate 10 is processed in a batch vertical diffusion furnace with DCE/O₂ (Trans 1,2-Dichloroethylene/Oxygen) gas. FIG. 1B is a side view of the resulting substrate 11 showing a base gate dielectric 12 comprising a chlorine (Cl) layer 13 on a silicon dioxide (SiO₂) layer 14. The substrate 11 is processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm². FIG. 1C is a side view of the resulting substrate 15 showing a dielectric 17 comprising an N layer 18 on the SiO₂ layer 14.

[0018] The DCE plays a critical role in the in-situ surface nitridation process as the incorporated Cl species is constrained to the surface of the grown gate oxide and undergoes a substitutional chemical reaction with the NH₃ species during the nitridation process. The substitutional chemistry between the Cl and NH₃ species enables maximum nitrogen incorporation, constraining the nitridation to the surface of the gate dielectric.

[0019] FIGS. 2A-D are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin nitric oxide (NO) based gate dielectric, in an embodiment in accordance with the invention.

[0020]FIG. 2A is a side view of a Si semiconductor substrate 10. The substrate 10 is processed in a batch vertical diffusion furnace with NO/N₂ gas. FIG. 2B is a side view of the resulting substrate 20 showing a base gate dielectric 21 comprising a SiON layer 22. The substrate 20 is re-oxidized in-situ with DCE/O₂ gas. FIG. 2C is a side view of the resulting substrate 23 showing a dielectric 24 comprising a Cl layer 13 on a SiON layer 22 on a SiO₂ layer 14. The substrate 23 is processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1 E-7 moles NH₃/mm². FIG. 2D is a side view of the resulting substrate 26 showing a dielectric 26 comprising an N layer 18 on a SiON layer 22.

[0021] The DCE plays a critical role in the in-situ surface nitridation process. After the NO gas forms the base gate dielectric of SiON, the SI substrate is re-oxidized via the DCE/O₂ gas. The incorporated Cl species is constrained to the surface of the grown SiON gate oxide and undergoes a substitutional chemical reaction with the NH₃ species during the in-situ nitridation process. The substitutional chemistry between the C-1 and NH₃ species enables maximum nitrogen incorporation, constraining the nitridation to the surface of the gate dielectric.

[0022] FIGS. 3A-D are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin “dry-wet” DCE/O₂-H₂O/O₂ based ultra-thin gate dielectric, in an embodiment in accordance with the invention.

[0023]FIG. 3A is a side view of a Si semiconductor substrate 10. The substrate 10 is processed in a batch vertical diffusion furnace with a “dry ox” DCE/O₂ gas. FIG. 3B is a side view of the resulting substrate 30 showing a base gate dielectric 31 comprising a Cl layer 13 on the SiO₂ layer 14. The substrate 30 is processed in-situ with H₂O/O₂ gas (wet ox). FIG. 3C is a side view of the resulting substrate 32 showing a dielectric 33 comprising a Cl layer 13 on a SiO₂ layer 14. The substrate 32 is processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm². FIG. 3D is a side view of the resulting substrate 35 showing a dielectric 36 comprising an N layer 18 on a SiO₂ layer 14.

[0024] The DCE plays a critical role in the in-situ surface nitridation process as the incorporated Cl species is constrained to the surface of the grown gate oxide and undergoes a substitutional chemical reaction with the NH₃ species during the nitridation process. The substitutional chemistry between the C₁ and NH₃ species enables maximum nitrogen incorporation, constraining the nitridation to the surface of the gate dielectric.

[0025] The H₂O/O₂ “wet” oxidation step provides a critical advantage to the gate edge leakage characteristic. A “wet” treatment provides additional gate edge thickness growth necessary to meet the 90 nm CMOS technology leakage requirements.

[0026] FIGS. 4A-D are side views of a Si substrate 10 undergoing in-situ ammonia nitridation of an ultra-thin “dry-wet” DCE/O₂—H_(20/0) ₂ based ultra-thin gate dielectric, in another embodiment in accordance with the invention.

[0027]FIG. 4A is a side view of a Si semiconductor substrate 10. The substrate 10 is processed in a batch vertical diffusion furnace with a “dry ox” DCE/O₂ gas. FIG. 4B is a side view of the resulting substrate 40 showing a base gate dielectric 41 comprising a Cl layer 13 on a SiO₂ layer 14. The substrate 40 is processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1 E-7 moles NH₃/mm². FIG. 4C is a side view of the resulting substrate 42 showing a dielectric 43 comprising an N layer 18 on a SiO₂ layer 14. The substrate 42 is processed in-situ with H₂O/O₂ gas (wet ox). FIG. 4D is a side view of the resulting substrate 44 showing a dielectric 46 comprising an N layer 18 on a SiO₂ layer 14.

[0028] By changing the specific processing order of the “dry”, “wet” and in-situ ammonia nitridation, a gate dielectric can be chemically tailored to incorporate different levels of nitridation at the gate dielectric surface, and alter the edge to area leakage characteristics to accommodate different CMOS technology transistor requirements.

[0029]FIGS. 5A and 5B presents graphs of data comparing the performance of DCE-based gate oxide in-situ nitridation and chemically tailored “dry-wet”-based gate oxide with in-situ nitridation, respectively, with the performance of traditional ex-situ rapid thermal anneal (RTA) processing. The ultra-thin chemically tailored gate dielectrics generated in a vertical diffusion furnace with ultra-dilute NH₃, below 1E-7 moles NH₃/mm², in-situ nitridation show a performance comparable or better to traditional ex-situ rapid thermal anneal (RTA) processing techniques for 90 nm CMOS technology. These methods, in accordance with embodiments of the present invention, replace and remove at least one process layer in the fabrication of CMOS devices using traditional ex-situ RTA processing, decreasing production costs, and improving fabrication cycle time, with equivalent or improved transistor performance.

[0030]FIG. 6 is a representation of a vertical diffusion furnace 60 (VDF) for in-situ nitridation and growth of ultra-thin gate dielectrics, in accordance with an embodiment of the present invention. The VDF is particularly useful for nitridation via an NH₃ (ammonia) or NO (Nitric Oxide) source. The VDF comprises: a RHC (rapid heat/rapid cool) thermal apparatus 61; an external pyro torch for DCE cracking 62; catalytic water (steam) vapor generator 63; NO (nitric oxide) source 64; NH₃ (ammonia) source 65; and N₂ reactor chamber dilution source. The semiconductor substrate are held horizontally in a frame 68, and are processed in a reaction chamber 69.

[0031] In an embodiment in accordance with the present invention, the VDF 60 comprises: an NO (nitric oxide) source 64 with a flow rate of less than 50 sccms; NH₃ (ammonia) source 65 with a flow rate of less than 50 sccms; and N₂ reactor chamber dilution source greater than 25 slm.

[0032] In an embodiment in accordance with the present invention, the VDF 60 produces pressure up to 25 atm (367 psi) and temperature up to 1100° C., with rapid pressure and temperature ramp capability, and with a multiple substrate batch processing capability. The substrate 67 are inserted into the reactor chamber 69 where they are left until the pressure drops to the 10⁻⁷ torr range. The substrate 67 are then annealed in vacuum to 850° C. for 30 minutes. In another embodiment, the substrate 67 are inserted into an introduction chamber (not shown) where they are left until the pressure drops to the 10⁻⁷ torr range. The substrate 67 are then transferred using a manipulator in the reaction chamber 69 where it is annealed in vacuum to 850° C. for 30 minutes. This process allows removal of residual hydrocarbons, oxides, and most other contaminants from the substrate 67 surface. The substrate 67 temperature is lowered to that appropriate for nitridation (600-750° C.), in accordance with the methods of the present invention. In another embodiment, following nitridation, a low temperature buffer layer is deposited at 450-550° C. with either ECR-MBE (ECR-N₂ and Ga), GSMBE (NH₃ and Ga), MOMBE (ECR-N₂ and TEG), or CBE (NH₃ and TEG).

[0033] Although specific embodiments have been illustrated and described herein for purposes of description of the preferred embodiment, it will be appreciated by those of ordinary skill in the art that a wide variety of alternate and/or equivalent implementations calculated to achieve the same purposes may be substituted for the specific embodiment shown and described without departing from the scope of the present invention. Those with skill in the art will readily appreciate that the present invention may be implemented in a very wide variety of embodiments. This application is intended to cover any adaptations or variations of the embodiments discussed herein. Therefore, it is manifestly intended that this invention be limited only by the claims and the equivalents thereof. 

What is claimed is:
 1. A method for ammonia nitridation of an ultra-thin DCE/O₂ (Trans 1,2-Dichloroethylene) based gate dielectric comprising: providing a Si substrate; processing the Si substrate in a furnace with DCE/O₂ (Trans 1,2-Dichloroethylene/Oxygen) gas forming a base gate dielectric comprising a chlorine (Cl) layer on a silicon dioxide (SiO₂) layer on the Si substrate; processing the Si substrate with an ultra-dilute NH₃/N₂ gas forming a dielectric comprising an N layer on the SiO₂ layer on the Si substrate.
 2. The method of claim 1, wherein processing the Si substrate comprises processing the Si substrate in a batch vertical diffusion furnace.
 3. The method of claim 2, wherein processing the Si substrate with an ultra-dilute NH₃/N² gas comprises: processing the Si substrate with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm².
 4. The method of claim 3, wherein processing the Si substrate with an ultra-dilute NH₃/N² gas at a concentration of less than 1E-7 moles NH₃/mm² comprises: processing the Si substrate in a batch vertical diffusion furnace processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1 E-7 moles NH₃/mm².
 5. The method of claim 1, further comprising prior to processing the Si substrate in a furnace with DCE/O₂ (Trans 1,2-Dichloroethylene/Oxygen) gas forming a base gate dielectric comprising a chlorine (Cl) layer on a silicon dioxide (SiO₂) layer on the Si substrate: drawing a pressure to about 10⁻⁷ torr; annealing at 850° C. for 30 minutes; lowering the temperature to between 600-750° C.
 6. A method for ammonia nitridation of an ultra-thin nitric oxide (NO) based gate dielectric, comprising: providing a Si substrate; processing the Si substrate in a furnace with NO/N₂ gas forming a base gate dielectric comprising a SiON layer on the Si substrate; re-oxidizing the Si substrate with DCE/O₂ gas forming a dielectric comprising a Cl layer on a SiON layer on a SiO₂ layer on the Si substrate; processing the Si substrate with an ultra-dilute NH₃/N₂ gas forming a dielectric comprising an N layer on a SiON layer on the Si substrate.
 7. The method of claim 6, wherein the Si substrate is processed in a batch vertical diffusion furnace.
 8. The method of claim 7, wherein re-oxidizing the Si substrate with DCE/O₂ gas comprises re-oxidizing the Si substrate in-situ with DCE/O₂ gas.
 9. The method of claim 8, wherein processing the Si substrate with an ultra-dilute NH₃/N₂ gas comprises: processing the Si substrate with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm².
 10. The method of claim 8, wherein processing the Si substrate with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm² comprises: processing the Si substrate in a batch vertical diffusion furnace processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1 E-7 moles NH₃/mm².
 11. The method of claim 6, further comprising prior to processing the Si substrate in a furnace with DCE/O₂ (Trans 1,2-Dichloroethylene/Oxygen) gas forming a base gate dielectric comprising a chlorine (Cl) layer on a silicon dioxide (SiO₂) layer on the Si substrate: drawing a pressure to about 10⁻⁷ torr; annealing at 850° C. for 30 minutes; lowering the temperature to between 600-750° C.
 12. A method for ammonia nitridation of an ultra-thin “dry-wet” DCE/O₂-H₂O/O₂ based gate dielectric, comprising: providing a Si substrate; processing the Si substrate in a furnace with a “dry ox” DCE/O₂ gas forming a base gate dielectric comprising a Cl layer on the SiO₂ layer on the Si substrate; processing the substrate with H₂O/O₂ gas (wet ox) forming a dielectric comprising a Cl layer on a SiO₂ layer on the Si substrate; processing the Si substrate with an ultra-dilute NH₃/N₂ gas forming a dielectric comprising an N layer on a SiO₂ layer on the Si substrate.
 13. The method of claim 12, wherein the Si substrate is processed in a batch vertical diffusion furnace.
 14. The method of claim 13, wherein processing the Si substrate with an ultra-dilute NH₃/N₂ gas comprises: processing the Si substrate with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm².
 15. The method of claim 12, further comprising prior to processing the Si substrate in a furnace with DCE/O₂ (Trans 1,2-Dichloroethylene/Oxygen) gas forming a base gate dielectric comprising a chlorine (Cl) layer on a silicon dioxide (SiO₂) layer on the Si substrate: drawing a pressure to about 10⁻⁷ torr; annealing at 850° C. for 30 minutes; lowering the temperature to between 600-750° C.
 16. A method for ammonia nitridation of an ultra-thin “dry-wet” DCE/O₂-H₂O/O₂ based ultra-thin gate dielectric, comprising: a Si substrate: processing the Si substrate in a furnace with a “dry ox” DCE/O₂ gas forming a base gate dielectric comprising a Cl layer on a SiO₂ layer on the Si substrate; processing the So substrate with an ultra-dilute NH₃/N₂ gas forming a dielectric comprising an N layer on a SiO₂ layer on the Si substrate; processing the Si substrate with H₂O/O₂ gas (wet ox) forming a dielectric comprising an N layer on a SiO₂ layer.
 17. The method of claim 16, wherein the Si substrate is processed in a batch vertical diffusion furnace.
 18. The method of claim 17, further wherein processing the Si substrate with an ultra-dilute NH₃/N₂ gas comprises: processing the Si substrate with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm².
 19. The method of claim 16, further comprising prior to processing the Si substrate in a furnace with a “dry ox” DCE/O₂ gas forming a base gate dielectric comprising a Cl layer on a SiO₂ layer on the Si substrate: drawing a pressure to about 10⁻⁷ torr; annealing at 850° C. for 30 minutes; lowering the temperature to between 600-750° C.
 20. The method of claim 16, wherein processing the Si substrate with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1E-7 moles NH₃/mm² comprises: processing the Si substrate in a batch vertical diffusion furnace processed in-situ with an ultra-dilute NH₃/N₂ gas at a concentration of less than 1 E-7 moles NH₃/mm².
 21. A vertical diffusion furnace for in-situ nitridation and growth of ultra-thin gate dielectrics, comprising: a frame adapted for simultaneous vertical processing of a plurality of substrate; a reaction chamber, the frame adapted to be placed vertically within the reaction chamber; a rapid heat/rapid cool thermal apparatus adapted to control the temperature of the reaction chamber; an external pyro torch for DCE cracking interconnected with the reaction chamber; a catalytic water vapor generator interconnected with the reaction chamber; a NO (nitric oxide) source interconnected with the reaction chamber; an NH₃ (ammonia) source interconnected with the reaction chamber; and a N₂ reactor chamber dilution source interconnected with the reaction chamber.
 22. The vertical diffusion furnace of claim 21, wherein the reaction chamber is adapted to produce pressure up to 25 atm (367 psi) and temperature up to 1100° C., and to provide a rapid pressure and temperature ramp capability. 